1. Field of the Invention
The present invention relates to a material applicable to a light-emitting element utilizing electroluminescence. Further, the present invention relates to a light-emitting element using the material and to a light-emitting device and an electronic device each using the light-emitting element.
2. Description of the Related Art
Organic compounds can take various structures compared with inorganic compounds, and it is possible to synthesize a material having a variety of functions by appropriate molecular design of an organic compound. Because of these types of advantages, attention has been focused on photo electronics and electronics in which functional organic compounds are used in recent years.
For example, as examples of electronic devices in which organic compounds are used as functional materials, there are solar cells, light-emitting elements, organic transistors, and the like. These devices use the electrical properties and optical properties of organic compounds. Among them, in particular, tremendous progress in light-emitting elements has been made.
It is said that the light emission mechanism of a light-emitting element is as follows: by application of a voltage between a pair of electrodes with a light-emitting layer interposed therebetween, electrons injected from a cathode and holes injected from an anode recombine in the luminescence center of the light-emitting layer to form excitons in molecules, and when the excitons in molecules relax to a ground state, energy is released to emit light. A singlet excited state and a triplet excited state are known as excited states, and it is thought that light emission can be obtained through either of the excited states.
In an attempt to improve the performance of such a light-emitting element, there are many problems depending on a material, and in order to solve these problems, improvement of an element structure, development of a material, and the like have been carried out.
For example, as an electron-transporting material for a light-emitting element, 2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI) or the like is widely used (see Reference 1: Y. T. Tao and three others, Applied Physics Letter, Vol. 77, No. 11, p. 1575, 2000). However, development of a material with more excellent characteristics such as further higher mobility has been demanded. In particular, in view of commercialization, a reduction in power consumption is an important object, and development of a material and a light-emitting element with more excellent characteristics has been desired.